The present invention relates to an object lens barrel that includes at least an object lens constructed of a plurality of lenses and retains the object lens, an object lens barrel drive unit and an optical information recording and reproducing unit.
In recent years, there has been an attempt to employ an object lens constructed of a plurality of lenses in order to achieve a high numerical aperture particularly in an optical information recording and reproducing unit.
Japanese Patent Laid-Open Publication No. HEI 4-355419 discloses an object lens barrel that includes at least an object lens for use in such an optical information recording and reproducing unit and retains the object lens. As shown in FIG. 13, this object lens barrel is provided with an object lens constructed of five lenses in total and a barrel 57 for retaining and fixing the lenses.
Such an object lens constructed of a plurality of lenses has conventionally been subjected to positioning by mechanical accuracy including the steps of determining an inter-lens distance by putting the lens surfaces of the lenses in contact with each other and performing decentering and tilting of the lenses by putting reference surfaces of the lenses in contact with the reference surface of each lens provided in the lens barrel and fixing the same.
However, there has been the problem that the object lens has not been able to bring performance into full play as an object lens because optical aberration exists merely through the positioning by mechanical accuracy.
In order to solve this problem, there has been considered a method for reducing spherical aberration by putting a ring-shaped spacer material between lenses and changing the thickness of the spacer material. However, such a method needs a lot of components and incurs an increase in weight of the object lens barrel. The inter-lens distance is specified by the thickness of the spacer material, and therefore, the inter-lens distance cannot be set to an arbitrary distance, also causing residual spherical aberration. Moreover, the fact that the object lens barrel employed for the optical information recording and reproducing unit has a heavy weight also leads to an increase in weight of the movable portion of an object lens barrel drive unit for driving the object lens barrel, consequently reducing an access speed with respect to an optical recording medium.
The present invention has been made in view of the aforementioned circumstances and has the object of providing an object lens barrel capable of easily executing inter-lens position adjustment and having a small number of components, an object lens barrel drive unit and an optical information recording and reproducing unit.
In order to achieve the above object, there is provided an object lens barrel comprising:
at least a combinational object lens constructed of a plurality of lenses including at least a first lens and a second lens, wherein `at least one of the first lens and a first lens barrel for retaining the first lens is fixed by bonding to at least one of the second lens or a second lens barrel for retaining the second lens via a spacer layer made of an adhesive.
According to the object lens barrel of the present invention, there can be executed inter-lens decentering, tilting and inter-lens distance adjustment as well as the arbitrary determination of the amount of adjustment, and therefore, the residual aberration can be reduced. Furthermore, the weight of the object lens is smaller than when a spacer of a metal or the like is employed.
Furthermore, according to the object lens drive unit of the present invention, the object lens barrel, which has a compact size and light weight, can be driven at high speed.
Furthermore, according to the optical information recording and reproducing unit of the present invention, the object lens barrel has a compact size and light weight. Therefore, high-speed access can be achieved by driving the object lens barrel at high speed. Furthermore, a high numerical aperture can be achieved, and this enables the recording and reproducing on a high-density optical recording medium.